Thin film in-line degasser

ABSTRACT

The invention is a stackable packing element for use in degassing liquid ophthalmic lens monomer, and to a modular degasser and process, including an in-line degassing process, employing same. The stackable packing element is comprised of a body module and a removable puck component.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to provisional application, U.S. Ser.No. 60/360,910, filed Mar. 1, 2002, and having the same title andincorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to the degassing of liquid monomerused in fabricating ophthalmic lenses, such as for example soft contactlenses. In particular, the invention concerns a packing element for adegasser. The packing element is modular, and adapted for stacking withother such modules. The invention provides increased flexibility formaking modifications to the degas operation by allowing convenientaddition, removal or replacement of such packing elements as may berequired in response to any given situation. Moreover, the packingelement of the invention can be more easily cleaned, which operation isfurther facilitated by the packing element being constituted ofremovable parts. The invention also permits in-line degassing of liquidmonomer, which increases ophthalmic lens production line efficienciesand mitigates environmental concerns associated with batch degassingprocesses commonly used.

2. Description of the Prior Art

Ophthalmic lenses, such as for example, soft contact lenses, can befabricated by a variety of techniques. The more industrially popularmethods involve the use of suitable liquid monomers, such ashydroxyethyl methacrylate (HEMA), that are deposited into especiallyconfigured mold halves. The monomer can be cured by any number oftechniques, e.g. ultraviolet radiation, to form the lens. The liquidmonomer, however, invariably contains dissolved gases such as oxygen andnitrogen, which can detrimentally affect curing either by formingunwanted bubbles, which can manifest as voids or other flaws in thefinal lens, or by otherwise interfering with the curing mechanismitself. It has thus become a common practice to degas the liquid monomerprior to use.

Accordingly, different techniques have been explored for degassing themonomer. One practice is to employ a rotary evaporator unit that removesexcess gas from the monomer by rotating same under subatmosphericpressure. The container holding the mixture is then flushed with andheld under nitrogen atmosphere. Another technique is described in U.S.Pat. No. 5,435,943 wherein the monomer is pumped through a gas permeabletube surrounded by a subatmospheric chamber. Gases in the monomerpermeate the tube in favor of the lower pressure on the outside of same,the degassed monomer then being deposited into the lens molds and cured.

While these methods have proven commercially useful, efforts to advancethe degas operation are nonetheless of interest. For example, the rotaryevaporator method provides an opportunity for nitrogen gas tore-dissolve into the monomer during back fill flushing. Degas usingpermeable tubing has its own drawbacks: it typically demands batchoperation due to the particulars involved in pumping viscous liquidmonomer through tubing; thus, monomer is stored in vessels untilrequired, whereupon it is sent to a tubular degas station which is offline. In a production environment where automation and advances inautomation are critical, the use of a batch operation causes numerousinefficiencies that can adversely affect yield and logistics. Related tothis is the fact that the permeable tubing is at some point subject tobreakage, due for example to the pressure difference on either side ofthe tube wall and wear of the material of construction, typicallysilicone tubing. Breakage usually results in a shut down and oftenrequires the wholesale replacement of tubing bundles, even those thatare still intact, the arduousness of which can further disruptoperations. Moreover, the permeable tubing typically can not be properlycleaned when the need arises given, for example, the difficulty ofcleaning the lumen. A batch degas operation also creates disposalproblems inasmuch as liquid monomers for ophthalmic lenses commonly haveshelf lives, and if not used within same they must be discarded.Moreover, in a batch operation where liquid monomer is pumped from astorage vessel, there is always some residual monomer remaining in thevessel after use. The aggregate amount of this residue, in the contextof an industrial production facility, must be disposed of once past itsshelf life.

There is thus a continuing need in the art for a degas technology thathas increased effectiveness in both operation and maintenance, whichtechnology can be employed in-line, and with reduced disposal issues.

SUMMARY OF THE INVENTION

The present invention satisfies the foregoing desiderata. The inventionis directed to a stackable packing element for a degasser employed todegas liquid monomer used to fabricate ophthalmic lenses. The stackablepacking element comprises:

a body module having a bottom surface with at least one holetherethrough and an upwardly directed sidewall peripheral to said bottomsurface and adapted for stacking with another body module, said bottomsurface and said upwardly directed sidewall defining a chamber; and

a puck having a top portion onto which said liquid monomer can flow, anda side member, said side member extending downwardly from said topportion to removably set said puck within said chamber, said side memberdefining at least one side opening through which said liquid monomer canflow from said top portion into said chamber and over said bottomsurface and through said at least one hole.

The invention also relates to a degasser comprised of a plurality ofsaid stackable packing elements, as well as a degassing processemploying same. The degasser can comprise modular packing elements.

Beneficially, the invention enables thin film flow of liquid monomerover the surfaces defined which allows direct contact of the monomerwith the vacuum environment or an inert environment, preferably in avacuum environment, under which the degasser operates, thus providingmore efficient degas than heretofore obtainable. The invention can alsobe implemented in-line with the production facility, thus eliminatingthe difficulties inherent to batch degas processing as set forthhereinabove. That is, using the invention, degassing can occurcontinuously with the degassed monomer being pumped directly to thedeposition station on the production line. Furthermore, by being modularin nature, the invention enables quick reconfiguration of the degasserby simply stacking more packing elements to, or conversely by simplyremoving same from the stack. Additionally, the modularity of thepacking elements and their surfaces are more easily cleaned than priorart devices; this is further facilitated by the packing element beingconstituted of removable parts.

In an alternative embodiment a plurality of stacking packing elementsare assembled within a container, such as a column, but not attached tothe container. Preferably, first and second packing elements alternatewithin the container. The packing elements have vertical supportsbetween horizontally extended pieces. The flow of the liquid is from theuppermost packing element to the lowermost packing element. Theplurality of stackable packing elements comprise at least twodifferently shaped modular packing elements that alternate in the stack.In the preferred embodiment, the flow of the liquid within the containeris from the center of a first packing element towards the periphery ofthe first packing element then to the periphery of a second packingelement located beneath the first packing element. The liquid then flowsfrom the periphery to the center of the second packing element undervacuum or an inert environment within the container. In this embodimentthe stackable packing elements do not themselves define the chamberswithin which a vacuum is established or through which an inert gas ispumped.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are perspective, bottom and side views,respectively, of an embodiment of a packing element, referred to as abody portion, of the invention.

FIGS. 2A, 2B, 2C and 2D are perspective, top and first and second sideviews, respectively, of an embodiment of a packing element of theinvention, referred to as a puck. This puck embodiment beingparticularly useful with body portion illustrated in FIG. 1.

FIG. 3 depicts a plurality of packing elements, in particular packingelements constituted of the body portion and puck embodimentsillustrated in FIGS. 1 and 2, stacked atop each other, with a top feedmodule delivering liquid monomer for degas, the figure furtherexemplifying the cascading flow of monomer through the packing.

FIGS. 4A, 4B and 4C are perspective, bottom and side views,respectively, of an embodiment of a top feed module for the invention,this embodiment being particularly useful with the packing elements ofFIG. 3.

FIGS. 5A, 5B, 5C, 5D and 5E are perspective, bottom and first, secondand third side views, respectively, of an embodiment of a reservoirmodule for the invention, this embodiment being particularly useful withthe packing elements of FIG. 3.

FIG. 6 depicts an embodiment of a modular degasser of the invention,said embodiment constituted of a plurality of packing elements asstacked in FIG. 3 with the embodiments of the top feed module andreservoir module of FIGS. 4 and 5 respectively.

FIGS. 7A, 7B and 7C are perspective, bottom and side views,respectively, of an alternative embodiment of a body portion for thepacking element of the invention.

FIG. 8 is a second embodiment of a degasser.

FIGS. 9A, 9B, and 9C are perspective, bottom and side views,respectively, of an alternative embodiment of a packing element of theinvention.

FIGS. 10A, 10B, and 10C are perspective, bottom and side views,respectively of an alternative embodiment of a packing element of theinvention to be used with the packing element shown in FIGS. 9A, 9B and9C in the degasser shown in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has particular utility in degassing liquid monomerused to fabricate ophthalmic lenses. Examples of ophthalmic lenses inthis regard include without limitation hard, soft, rigid gas permeablecontact and intraocular lenses, and lenses for eyeglasses. The inventionhas especial utility for soft contact lenses commonly classified ashydrogel lenses; and for the liquid monomers from which these aregenerally prepared including but not limited to hydroxyethylmethacrylate (HEMA), vinyl pyrrolidone, glycerol methacrylate,methacrylic acid and acid esters. For purposes of this specification,the term “liquid monomer” includes monomers as aforesaid, mixtures ofsame, including mixtures of any or all of the above with other additivesknown in the art, such as for example, cross-linking and strengtheningagents. Gases typically dissolved in said liquid monomer to whichremoval (degassing) is sought include oxygen and may include nitrogen,and other gases. While not constraining the present invention, softlenses in this regard are typically prepared by free radicalpolymerization of monomer mix in a plastic mold having male and femalehalves of predetermined shape and characteristic. Polymerization isconventionally initiated by thermal means, or is photoinitiated usingeither UV or visible radiation.

The present invention will now be described in the context of thepreferred embodiments illustrated in FIGS. 1-6, it being understood thatother embodiments and practices consistent with this description arecontemplated as being within the scope the inventive practice delineatedhereinunder. The present invention involves packing elements, preferablystackable packing elements for degassing as aforesaid. The packingelements can comprise multiple shapes, preferably repeating modularshapes. In this embodiment the stackable packing elements comprise abody module and a removable puck component. While these can be of anyshape, e.g. circular, oval, square, rectangular, triangular and otherpolygonal shapes, it is preferred that they are generally circular. FIG.1 shows a preferred embodiment of said body module. As depicted in FIG.1A, body module 10 (shown in an upside down perspective in FIG. 1A) hasa bottom surface 11 (the underside of which is denoted 11 a in FIG. 1A)that has at least one hole 12 therethrough. Preferably, the bottomsurface has a plurality of holes therethrough, more preferably theseholes are centrally located on the bottom surface, e.g. located at, nearor around the center of the bottom. In a more preferred practice, theplurality of holes 12 are located around the center of bottom 111 andequally spaced around same. In one embodiment, illustrated in FIG. 1Aand in FIG. 3, the plurality of holes are located around the center ofthe bottom surface 11 and pass through same at an angle. Preferably theangle of each hole, which angle can be the same or different, convergestoward the center line of bottom 11 as it passes therethrough, e.g. eachof the four holes 12 depicted in FIGS. 1A and 1B pass through the bottomsurface 11 at an angle of about 45° normal to the center line of bottom11 (see also FIG. 3).

Body module 10 further has an upwardly directed sidewall 13 peripheralto the bottom surface. The sidewall is adapted for stacking; that is, itis constructed such that the body module of one packing element can bestacked on top of, or below, another such packing element. Adaptationsfor stacking in the context of the invention include those known in theart, e.g. the use of appropriately sized indentations, protrusions,interlocking, overlapping configurations and the like. A preferredadaptation for stacking is shown in FIG. 1C and FIG. 3. In thisembodiment, sidewall 13 has a lower portion, generally 13 a, and anupper portion, generally 13 b, which are juxtaposed so as to form afirst notch 13 aa that extends around the external periphery (here, theouter circumference) of lower portion 13 a; and a second notch 13 bbextends around the internal periphery (here, the inner circumference) ofupper portion 13 b. In one practice, the cylindrical portion of sidewall13 that is formed by notch 13 aa has a diameter smaller than that forthe cylindrical portion of sidewall 13 formed by notch 13 b, such thatit can fit into (be overlapped at least in part by) same in a sleevefashion, as shown for example in FIG. 3, thus enabling body modules 11(hence the packing elements comprising same) to be stacked, one on topof the other. Preferably, the cylindrical portion of sidewall 13 formedby notch 13 aa has means to secure a gasket or other sealing material,preferably a groove 15 (FIG. 3) into which a gasket ring 16 (FIG. 6),such as Viton® and like materials, can be placed.

The bottom surface 11 and upwardly directed sidewall 13 together definea chamber 14, within said body module. In the preferred practice shownin FIG. 1 and FIG. 3 this chamber is cylindrical in shape and closed atbottom surface 11 but for hole(s) 12. The sealing material forms a sealbetween the body modules that define a series of air-tight chambers inthe degasser when the vacuum or other lower pressure environment (lowerpressure than atmospheric pressure) is established. Alternativelymechanical means, such as a clamp, an adjustable band, weights can beused to keep the packing elements in a sealed arrangement, particularlywhen a lower pressure, e.g. vacuum, environment is not created withinthe degasser. Other mechanical means include the provision of matingthreaded or grooved parts of the packing elements that can be screwed orsnapped together to form a seal between the body modules or otherpacking elements. For example, threads (not shown) can be added in thelower portion 13 a and upper portions 13 b of the side walls of the bodymodules; the threads can be screwed together to form an air-tightchamber in the degasser. Other parts of the degasser, e.g. top feedmodule and reservoir module would be provided with or held in anair-tight relationship with the packing elements by the same ordifferent, preferably the same, mechanical means. This embodiment isespecially useful when an inert environment is created in the degasser.An inert environment would include nitrogen, argon or the like.

FIG. 2 shows a preferred embodiment of a puck component which togetherwith the body module aforesaid comprise the inventive packing element.In the practice depicted in FIG. 2A, puck 20 has a cap or cap-like shapeand has a top portion 21 and a side member 22 which extends downwardlyfrom the top portion. It will be appreciated that in a preferredpractice the geometry of the body module and that for the puck will besimilar. For example, in FIG. 1 the body module is generally circular,hence in a preferred practice the puck will also be generally circular,as indicated in FIG. 2. Dimensionally, the puck is preferably of a sizeto fit within chamber 14, preferably, to not extend into the regiondefined by upper sidewall portion 13 a, as delimited for example bynotch 13 aa, in which region stacking occurs as described above. Topportion 21 preferably has a substantially flat upper surface. Sidemember 22 is designed to permit the puck to be removably set withinchamber 14. For example, and without limitation, the side member can beconfigured to freely stand puck 20 within chamber 14. Preferably, theside member is configured to stand top portion 21 away from the bottomsurface 11 and preferably away from hole(s) 12. Side member 22 furtherdefines at least one side opening 24. Preferably, a plurality of sideopenings are so defined; more preferably, they are equally spaced alongthe periphery (here, the circumference) of puck 20. Suitable sidemembers include a skirt with one or more side openings, or a pluralityof projections, e.g. legs, struts and the like, the areas between whichdefine the side openings. In the practice shown in FIG. 2 side member 22appears as a plurality of projections defining a plurality of sideopenings 24. Preferably, as illustrated in FIG. 2, each of the sidemembers among themselves have approximately the same circumferentiallength, as do the side openings. More preferably, each side member andeach side opening as between each other have the approximately the samecircumferential length. In one practice, shown e.g. in FIG. 2B, thereare four side members 22 each of the same circumferential length (thatis, as shown, each takes up about ⅛th of the circumference) and eachequally spaced apart along the circumference so as to define four sideopenings each having approximately that same length. In one embodiment,as exemplified in FIGS. 2C and 2D, side members 22 extend downward at anoutward slant from the top portion 21.

Functionally, as illustrated in FIG. 3, liquid monomer 30 is fed intothe packing element, either from a top feed module 40 or from a packingelement stacked above, flows onto the top portion 21 of the puck, downsame and into chamber 14, over bottom surface 11 and through hole(s) 12(the cascading flow streams of said liquid monomer as it traverses thepacking elements is shown by the bold flow lines in FIG. 3). Monomerexiting said hole(s) 12 can serve as feed to the packing elementthereunder or can feed into a reservoir module where it is collected, anembodiment of which is shown in FIG. 5 wherefrom it then is pumped,preferably in a pulsed or continuous fashion, to the production lineusing, e.g. one or more peristaltic pumps. Rheologically, in flowingthrough the packing element of the invention, a thin film of monomer iscreated, e.g. on the top surface of the puck and the bottom surface ofthe chamber. This thin film of monomer containing dissolved gases is indirect contact with the vacuum or inert environment under which thepacking element operates for degassing purposes. The dissolved gasesevaporate into the vacuum or inert environment and are removed from thepacking element in the vacuum or inert stream. In a preferred practice,the top portion 21 of puck 20 has a lip 23 therearound, which lipenables the liquid monomer to pool (to an extent given it is under flow)on the top surface. This pooling permits extended contact with thevacuum environment and thus facilitates degassing. In a preferredembodiment of this practice, as seen in FIGS. 2C, 2D and 3, the externaledge of lip 23 is outwardly slanted to assist fluid flow down into thechamber.

FIG. 4 shows a preferred top feed module 40 for use with the packingelements in forming a degasser as contemplated by the invention. FIG. 4Ashows a perspective view (of the underside 44 of the feed module) ofsaid feed module which has one or more liquid monomer feed inlets 42 andone or more outlets 41 from which vacuum is pulled. In a preferredpractice, the feed inlet has a downcomer 43 (FIGS. 3 and 6) to assist indirecting flow to the top portion of the puck thereunder. In anotherpreferred embodiment, top feed module 40 has a sidewall that is adaptedto stack with the packing elements, e.g. top module 40 has a notch 45(FIG. 4C) extending around the periphery of its sidewall which, as shownin FIG. 3, fits into the overlapping cylinder defined by upper sidewallportion 13 a of the packing element. In a preferred practice, thepacking element immediately beneath the top feed module does not have apuck component; that is, only the body portion is utilized at thispoint, as shown in FIG. 3. Top feed module 40 is also advantageouslydesigned with means to secure a gasket, such as groove 15 (FIG. 3).

FIG. 5 shows a preferred reservoir module 50 into which degassed liquidmonomer flows and is collected and pumped for dosing into the lens moldhalves to form the ophthalmic lens. Reservoir 50 is preferably the lastmodule in the degasser, as shown in FIG. 6. Reservoir module 50 ispreferably provided with one or more degassed liquid monomer outlets 52which are connected to one or more pumps (not shown), preferablyperistaltic pumps as commercially available. The use of one or moreoutlets 52 and one or more pumps especially facilitates pumpingoperations when the degasser and reservoir 50 are operating under vacuumand/or the liquid monomer is viscous. In another preferred embodiment,reservoir module 50 has a sidewall that is stackably adapted to thepacking elements, e.g. reservoir module 50 has a notch 51 (FIGS. 5C, 5Dand 5E, which are each side views of the reservoir rotated 90° eachtime, respectively) extending around the periphery of its sidewallwhich, as indicated in FIG. 6, fits around and overlaps the cylinderdefined by lower sidewall portion 13 b of the last packing element.

FIG. 6 shows an embodiment of the modular degasser of the inventionconstituted of the preferred packing elements and top feed and reservoirmodules of FIGS. 1-5. The modular degasser 60 is preferably operatedunder vacuum (i.e. subatmospheric conditions) and is constituted of aplurality of packing elements subject of the invention, as comprised ofbody modules 10 and pucks 20. Thus the height (the number of packingelements) of degasser 60 can be increased or decreased by simpleaddition or removal of packing elements. As appreciated by those ofskill in the art, the height of degasser 60 depends among other thingson the level of dissolved gases targeted to remain in the liquid monomerafter degassing, and also on the viscosity of the liquid monomer itself.Hence it will be understood that the lower the final level of dissolvedgas, e.g. oxygen and the like, desired and/or the higher the viscosityof the liquid monomer, the greater the number of packing elements thedegasser needs. The level of dissolved gases remaining in the liquidmonomer after degassing can be monitored using methods known in the art,which monitoring in turn can indicate when an increase or decrease inthe number of packing elements is required. Operationally, vacuum ispulled on degasser 60 through outlet(s) 41 using means known in the art;typical vacuum ranges in terms of absolute pressure are about 20millibar to about 100 millibar, it being understood that higher andlower pressures are contemplated. In a preferred practice, the liquidmonomer is essentially free of dissolved gases after degassing with thepresent invention.

In an alternative embodiment, the packing elements may comprisealternating body modules 10 as shown in FIGS. 1A, 1B, and 1C, and bodymodules 70 shown in FIGS. 7A, 7B and 7C, with or without additionalpucks or baffles added between the body modules. As shown body module 70is similar to body module 10 except that the holes 72 shown in bodymodule 70 are located around the circumference of the bottom of the bodymodule. In an embodiment consisting of alternating body modules 10 and70, the holes 12 and 72 direct the monomer or any other reactive mixtureacross the surface of the body modules and either down through thecenter of the body module as shown in FIG. 1 or through the holeslocated around the circumference of the body module as shown in FIG. 7.Alternatively, the holes may be located on opposite sides (180 degrees)across the body modules and the flow may be across the body modules, anddown to the next body module. The body modules may have alternativeshapes to those shown herein.

Preferred materials of construction for the packing element of theinvention, including the body module and puck, and further including thetop feed module and reservoir, include without limitation polymericmaterial, such as for example only, engineering grade plasticsServiceable polymeric materials include, without limitation to the scopeof possible materials, polyacetyls (e.g. Delrin®, which is mostpreferred), polystyrenes, polypropylenes, polyethylenes,polyetheretherketones (PEEK), polyamides (e.g. Nylon®), polyimides,polyamideimides (PAI), polyfluoroethylenes (e.g. Teflon®),polyetherimides, polyesters, polycarbonates, polyethers,polyetherimides, polysulfide polymers, polysulfones, and blends andalloys of the foregoing.

Alternatively, the packing elements shown in FIGS. 9 and 10 can be usedin a column shown in FIG. 8. The packing elements are designed as in theearlier embodiments except that they do not define the air-tight chamberwithin which the vacuum or inert environment is established. The packingelements are instead assembled within a container, e.g. the column shownin FIG. 8, and the vacuum or inert environment is established within thecontainer. The packing elements define surfaces that direct the liquidtowards the center of the first packing elements and out to theperiphery of the second packing elements, or in the alternative flowpatterns described above. The packing elements are not attached to thedegasser container and if desired can be shaped so that no liquid undernormal operating conditions will touch the inside of the column, exceptif desired for a reservoir at the bottom accumulated after the liquidflows through the stack of packing elements.

The packing element shown in FIGS. 9A, 9B and 9C can be assembled in analternating arrangement with the packing element shown in FIGS. 10A,10B, and 10C. The packing element 90 is shaped to direct the liquid tothe center of the packing element where holes 91 direct the flow ofliquid to the packing element below. The packing element 90 has legs orother supports 92 which support the flow surface 93 above the packingelement located beneath packing element 90. Notches, dimples, bumps orthe like can be provided on surface 101 to receive the supports 92 ifdesired to provide stability to the stacked packing elements. As shown,packing element 90 preferably has a lip 94 that directs the liquid awayfrom the walls of the container and towards the center of the surface93. Surface 93 is preferably slanted towards the holes 91; however, itis preferred that the surface 93 is substantially horizontal. In thisembodiment, preferably the packing element 100 shown in FIGS. 10A, 10B,and 10C is located beneath the packing element 90. (Packing element 90is supported and stacked upon packing element 100.) Packing element 100preferably comprises a flat or substantially flat surface 01 supportedby legs or other supports 102 that preferably keeps the surface 101spaced from the surface of the packing element located beneath packingelement 100. The liquid from packing element 90 hits the center ofsurface 101 and then flows out towards the periphery 103 of the surface101 of packing element 100. Then the liquid preferably flows to anotherpacking element 90 located beneath packing element 100. Notches,dimples, bumps or the like can be provided on surface 101 to receive thesupports 92, if desired to provide stability to the stacked packingelements.

In a preferred embodiment to keep the inside walls of the containerclean, preferably the liquid only contacts packing elements 90 and 100,and not any inside surfaces of the container. In this way thisembodiment provides the simple clean-up that is provided by the earlierembodiments. The stack of modular packing elements preferably consistingof alternating packing elements 90 and 100 can be removed from thecolumn and washed separately in a dish washer or the like and thenreassembled inside the column without having to mechanically remove orattach any of the packing elements to the column or other container. Thepacking elements are only stacked one on top of the other which makesassembly and disassembly easy for cleaning. If the column must becleaned it can be easily cleaned with a pipe cleaner. Missing detailsfor this embodiment can be the same as or similar to details describedfor the earlier embodiments.

The column can be made of any of the materials used in the prior art tomake degas columns, such as, glass, and engineering grade plastics.Serviceable polymeric materials include, without limitation to the scopeof possible materials, polyacetyls (e.g. Delrin®, which is mostpreferred), polystyrenes, polypropylenes, polyethylenes,polyetheretherketones (PEEK), polyamides (e.g. Nylon®), polyimides,polyamideimides (PAI), polyfluoroethylenes (e.g. Teflon ®),polyetherimides, polyesters, polycarbonates, polyethers,polyetherimides, polysulfide polymers, polysulfones, and blends andalloys of the foregoing. Depending upon the liquid to be degassed, andor the amount of contact between the metal and the liquid to bedegassed, metals might be useful, although presently not preferred.

What is claimed is:
 1. A stackable packing element for a degasser forliquid monomer used to make ophthalmic lenses which comprises: a bodymodule having a bottom surface with at least one hole therethrough andan upwardly directed sidewall peripheral to said bottom surface andadapted for stacking with another body module, said bottom surface andsaid upwardly directed sidewall defining a chamber; and a puck having atop portion onto which said liquid monomer can flow, and a side member,said side member extending downwardly from said top portion to removablyset said puck within said chamber, said side member defining at leastone side opening through which said liquid monomer can flow from saidtop portion into said chamber and over said bottom surface and throughsaid at least one hole.
 2. The stackable packing element of claim 1wherein said bottom surface has a plurality of holes therethrough, saidholes being centrally located on the bottom surface.
 3. The stackablepacking element of claim 2 wherein said plurality of holes each passthrough said bottom surface at an inclined angle.
 4. The stackablepacking element of claim 1 wherein said top portion of said puck has asubstantially flat upper surface onto which said liquid monomer canflow, said top portion having a lip therearound.
 5. The stackablepacking element of claim 4 wherein said side member comprises aplurality of spaced projections that extend downward at an outward slantfrom said top portion.
 6. The stackable packing element of claim 1wherein said sidewall is adapted for stacking by having a first notchextending around the periphery of a lower portion of said sidewall and asecond notch extending around the periphery of an upper portion of saidsidewall, said first notch configured to mate with the second notch onanother body module.
 7. The stackable packing element of claim 6 whereinsaid first notch extends around the external periphery of said lowerportion of said sidewall, and said second notch extends around theinternal periphery of said upper portion of said sidewall, said firstnotch configured to fit within the second notch said another bodymodule.
 8. A modular degasser for degassing liquid monomer used to makean ophthalmic lens, said modular degasser having a plurality of packingelements stacked together, each of said packing elements comprising: abody module having a bottom surface with at least one hole therethroughand an upwardly directed sidewall peripheral to said bottom surface andadapted for stacking with another body module, said bottom surface andsaid upwardly directed sidewall defining a chamber; and a puck having atop portion onto which said liquid monomer can flow, and a side member,said side member extending downwardly from said top portion to removablyset said puck within said chamber, said side member defining at leastone side opening through which said liquid monomer can flow from saidtop portion into said chamber and over said bottom surface and throughsaid at least one hole.
 9. The modular degasser of claim 8 wherein saidat least one hole is situated such that liquid monomer flowing throughsame forms the liquid monomer flow onto the top portion of the puck ofthe packing element stacked thereunder.
 10. The modular degasser ofclaim 9 further comprising a top feed module having inlet means forfeeding liquid monomer to said degasser, and outlet means situated suchthat said liquid monomer from said outlet means forms the liquid monomerflow onto the top portion of the puck of the packing element locatedunder said top feed module.
 11. The modular degasser of claim 10 whereinsaid outlet means further comprises a downcomer.
 12. A process fordegassing liquid monomer used for fabricating ophthalmic lenses, saidprocess comprising: providing a feed of liquid monomer to a modulardegasser operating under vacuum, said degasser having a plurality ofpecking elements stacked together, each of said packing elementscomprising: a body module having a bottom surface with at least one holetherethrough and at upwardly directed sidewall peripheral to said bottomsurface and adapted for stacking with another body module, said bottomsurface and said upwardly directed sidewall defining a chamber; and apuck having a top portion onto which said liquid monomer flows forming athin film, and a side member, said side member extending downwardly fromsaid top portion to removably set said puck within said chamber, saidside member defining at least one side opening through which said liquidmonomer flows in a thin film from said top portion into said chamber andover said bottom surface and through said at least one hole, said liquidmonomer passing through said at least one hole providing the liquidmonomer flow onto the top portion of the packing element thereunder,said liquid monomer being degassed as it flows through said packingelements; and collecting degassed liquid monomer feed from saidplurality of packing elements.
 13. The process of claim 12 wherein theproviding of said liquid monomer feed to the degasser is via a top feedmodule.
 14. The process of claim 13 wherein said collecting occurs in abottom reservoir module under the last packing element of said pluralityof packing elements.
 15. The process of claim 14 further comprising thestep of pumping the degassed liquid monomer from said bottom reservoirto a dosing station wherein said degassed liquid monomer feed isdeposited into a lens mold half.
 16. The process of claim 15 whereinsaid providing of liquid monomer feed, said collecting of degassedliquid monomer and maid pumping is continuous.
 17. The process of claim16 wherein the process is in-line to an ophthalmic lens production line.18. A degasser useful for degassing a liquid under a vacuum comprising:a first packing element and separate second packing element; said firstpacking element is stacked on top of said second packing element anddirects the flow of said liquid from said first packing element to saidsecond packing element; said first packing element comprises a surface;said second packing element comprises a surface; and wherein said atleast one of said first and second packing elements further comprisesupports to maintain the surfaces of the first and second packingelements separated.
 19. The degasser of claim 18, further comprising acontainer into which said first packing element and said second packingelement are stacked on top of each other and placed therein.
 20. Thedegasser of claim 18, wherein said at least one of said first packingelement or second second packing element comprises sidewalls defining achamber.
 21. The degasser of claim 18, wherein said surfaces of saidfirst packing element and second packing element are substantiallyhorizontal.